#' Centering a data matrix
#' Takes data matrix with each columns as variabes and center each columns
#' @param M a real matrix with variables stored in columns
#' @return Centered Data matrix
#' @export 
center_data_matrix<-function(M){
  #return(M-t(replicate(dim(M)[1],(apply(M,2,"mean")))))
  return(t(t(M)-(apply(M,2,"mean"))))
}